Various substituted 1,4-benzodioxines were synthesized through
an Ullmann-type intramolecular Caryl-O coupling
cyclization reaction using a catalytic amount of BINOL-CuI
complex. This methodology was successfully utilized as the key step
in the total synthesis of isovanillyl sweetening agents 5-(2,3-dihydro-1,4-benzodioxin-2-yl)-2-methoxyphenol
and 5-(2,3-dihydro-1,4-benzoxathiin-2-yl)-2-methoxyphenol
in 15.8% and 14.85% overall yields in five steps
from isovanillin.
copper catalyst - 1,4-benzodioxines - BINOL
ligand - Ullmann-type coupling - C-O bond
formation